Pandi1981 created an issue (kamailio/kamailio#4208)

We are facing an issue while using TOPOS in Kamailio P-CSCF (running under Docker). Kamailio version: 6.0.0 operating system: "10 (buster)"

**Call Flow & Issue Description:** Note: Public IP and Private IP mapping using the below configuration.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ listen=udp:LOCAL_IP:5060 name "internal" listen=udp:LOCAL_IP:6080 advertise PUBLIC_IP:6080 name "external" ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

**Call Flow (INVITE):**

A-Party --> Kamailio P-CSCF (Public IP) --> Kamailio P-CSCF (Private IP) --> Kamailio S-CSCF (Private IP) B-Party <-- Kamailio P-CSCF (Public IP) <-- Kamailio P-CSCF (Private IP) <-- Kamailio S-CSCF (Private IP)

Everything works correctly up to the point where the 200 OK is received by the A-Party. However, when the A-Party sends the ACK, it is received by the Kamailio P-CSCF but is not forwarded to the B-Party.

Upon investigation, we found that when Kamailio receives the ACK from the A-Party, the rr (Record-Route) module fails to recognize its own Route header and thus falls back to strict routing instead of performing loose routing. This results in an incorrect rewrite of the Request-URI of the ACK, causing it to fail to reach the B-Party. Essentially, the Route header is not popped as expected and the ACK routing breaks.

TOPOS module is configured as follows: loadmodule "topos_redis.so" loadmodule "ndb_redis.so" loadmodule "topos.so"

modparam("ndb_redis", "server", "name=tps;addr=127.0.0.1;port=6379;db=0") modparam("topos", "storage", "redis") modparam("topos_redis", "serverid", "tps")

modparam("topos", "rr_update", 1) modparam("topos", "contact_mode", 1) modparam("topos", "xavu_field_a_contact", "a_contact") modparam("topos", "xavu_field_b_contact", "b_contact") modparam("topos", "xavu_cfg", "tps")

Please guide us how to achieve and what we are doing wrong.